Therapeutic use of radioactive isotopes

A study published in collaboration with ISOLDE-CERN confirms that certain terbium isotopes are effective in diagnosing and treating tumours


In December, researchers from ISOLDE-CERN, the Paul Scherrer Institute (PSI) and the Institut Laue-Langevin (ILL) published results of an in vivo study that successfully proved the effectiveness of four terbium isotopes for diagnosing and treating cancerous tumours.

“ISOLDE is the only installation capable of supplying terbium isotopes of such purity and intensity in the case of three out of the four types used in this study,” says ISOLDE physicist Karl Johnson. “Producing over a thousand different isotopes, our equipment offers the widest choice of isotopes in the world!” Initially intended for fundamental physics research, ISOLDE has diversified its activities over time to invest in various projects in the fields of materials science, biochemistry and nuclear medicine.

The proof-of-concept study has confirmed that the four terbium isotopes 149Tb, 152Tb, 155Tb produced by ISOLDE and 161Tb produced by ILL can be used in matched pairs to simultaneously diagnose and treat tumours. Having attached itself to a cancerous cell, one of the isotopes emits radiation detectable by medical imaging instruments while the other produces short-range radiation that destroys the surrounding cells. This makes it possible to monitor the status of the cancerous tumour throughout the patient’s treatment and to adapt the prescribed terbium isotope dose accordingly.

“Although the first clinical trials with terbium isotopes were performed in the 1990s, the project only really took concrete form two years ago when activities started in the framework of the PSI-ILL-ISOLDE collaboration,” says Johnston. “The main difficulties were logistic rather than of a physics nature. For instance, as isotopes have very short lifetimes, it was essential to reduce the time lag between their production and their use by medical staff to the absolute minimum. So the laboratories performing the clinical tests had to be located no more than three hours away by car! We therefore had to produce the terbium samples between 4am and 8am, and pack the samples within 30 minutes with the help of CERN's Radiation Protection Group. If everything went according to plan, the isotopes were delivered to the PSI laboratories by 11.30am.”

This proof-of-concept study, jointly carried out by experts in the physics and nuclear medicine fields, has confirmed the therapeutic and diagnostic potential of terbium. However there is a long way to go before terbium can be used in hospitals because the quantities produced by ISOLDE are too small to allow large-scale statistical studies to be performed. Such studies will have to wait until June 2014, when activities resume after performance-enhancement upgrades during the LHC shutdown.

Terbium (Tb) is the only element in the Mendeleev periodic table that has four isotopes suitable for clinical purposes. The nuclear decay characteristics of these four isotopes mean that all the nuclear medicine procedures can be covered. 155Tb and 152Tb emit gamma rays detectable by gamma cameras or PET scanners. While 161Tb produces, inter alia, beta minus particles that damage the surrounding cells over a few millimetres, 149Tb produces short-range alpha particles that allow very localized destruction of the cancerous cells.

Find out more in the press release from the Institut Laue-Langevin.